Optical device and method therefor

Abstract

A photedetector uses a semiconductor on insulator (SOI) substrate having an optical grating over the silicon semiconductor to change the direction of incident light to divert it into the silicon which functions as waveguide. The underlying insulator operates as one boundary of the waveguide and the overlying grating operates as the other. Photodetector electrodes are placed in the silicon, which puts them in close proximity to the carriers that are generated by the light entering the silicon waveguide.

What is claimed is:  
     
       1. An optical device comprising: 
       a substrate comprising an insulating layer, an active semiconductor region above the insulating layer and a non-active semiconductor region below the insulating layer;  
       a detector within the active semiconductor region and over a first portion of the insulating layer; and  
       a grating over at least a portion of the detector.  
     
     
       2. The device of  claim 1  wherein the insulating layer is silicon dioxide. 
     
     
       3. The device of  claim 2  wherein the active semiconductor region is lightly-doped silicon-on-insulator. 
     
     
       4. The device of  claim 1  wherein the non-active region is lightly-doped silicon. 
     
     
       5. The device of  claim 1  wherein the active semiconductor region between the insulating layer and the grating portion form a waveguide. 
     
     
       6. The optical device of  claim 1  further comprising processing circuitry over a second portion of the insulating layer. 
     
     
       7. The device of  claim 6  wherein the processing circuitry comprises gates and interconnects and source and drain regions. 
     
     
       8. The device of  claim 7  wherein the gates and interconnects are formed over the active region and the source and drain regions are formed within the active region. 
     
     
       9. The device of  claim 1  wherein the detector comprises heavily-doped regions and lightly-doped regions. 
     
     
       10. The device of  claim 8  wherein the lightly-doped regions are doped at a concentration less than or equal to approximately 10 14  atoms/cm 2 . 
     
     
       11. The device of  claim 8  wherein a first portion of the heavily-doped regions is doped p-type and a second portion of the heavily-doped regions is doped n-type. 
     
     
       12. The device of  claim 10  wherein a heavily-doped region of the first portion is separated from a heavily-doped region of the second portion by a lightly-doped region. 
     
     
       13. The device of  claim 1  wherein the grating comprises a plurality of features. 
     
     
       14. The device of  claim 13  wherein the plurality of features have an approximate shape selected from the group containing a pyramid, a hexagon, a hemisphere, and a line. 
     
     
       15. A method for operating an optical device comprising: 
       providing a light at an angle to a substrate, wherein the substrate comprises an insulating region and an active region above the insulating region;  
       directing the light to the semiconductor device in the active region;  
       biasing a detector having doped regions in the active region;  
       collecting carriers in the active region to define a signal, wherein the carriers are generated by the light in the active region; and  
       processing the signal.  
     
     
       16. The method of  claim 15  wherein the angle is at a right angle. 
     
     
       17. The method of  claim 15 , wherein the active region further comprises a lightly doped region and wherein biasing the detector is further defined as causing the lightly doped region to be fully depleted. 
     
     
       18. A method of forming an optical device comprising: 
       providing a semiconductor substrate wherein the substrate comprises an insulating layer;  
       forming a detector over a first portion of the insulating layer;  
       forming a grating over a portion of the detector; and  
       forming process circuitry over a second portion of the insulating layer.  
     
     
       19. An optical device comprising: 
       a substrate comprising a silicon-on-insulator region comprising an insulating region and a silicon region over the insulating region;  
       a waveguide portion within at least a portion of the silicon region;  
       a detector within the waveguide portion, wherein the detector comprises a plurality of heavily-doped regions; and  
       a diffraction grating comprising a plurality of features over at least a portion of the detector.  
     
     
       20. The optical device of  claim 19 , wherein the diffraction grating comprises features comprising silicon. 
     
     
       21. The optical device of  claim 19 , wherein the waveguide is disposed between the diffraction grating and the insulating region. 
     
     
       22. A diffraction grating coupler structure comprising: 
       a first material, with a first refractive index;  
       a second material over the first material, wherein the second material has a second refractive index and the second refractive index is greater than the first refractive index; and  
       a third material over the second material with a third refractive index, wherein the third material comprises a plurality of features, wherein the plurality of features are approximately equidistant from each other and have an approximate shape selected from the group containing a pyramid and a hemisphere.  
     
     
       23. The diffraction grating coupler structure of  claim 22 , wherein the plurality of features comprise the hemisphere shape and are in a hexagonal pattern.